The present invention relates to an industrial robot which employs direct drive operation, whereby an arm carrying a manipulating member is directly driven by motors which are coupled directly thereto, without utilizing an intermediate speed reduction mechanism.
A prior art example of such a direct drive robot is shown in FIG. 1, in which reference numeral 1 denotes a base, with a first arm 2 being rotatably mounted on base 1 at one end of arm 2. A second arm 3 is rotatably mounted at one end thereof on the other end of the first arm 2. A hand mechanism 4, which includes a plurality of drive shafts for producing rotation and vertical displacement of a shaft 4a and a chuck 4b attached thereto, is mounted at the other end of the second arm 3. A first prime mover (not shown in the drawing) is mounted in the base 1, for directly driving the first arm 2 without employing an intermediate speed reduction mechanism. A second prime mover (not shown in the drawing), mounted within the first arm 2, drives second arm 3 to produce movement thereof relative to first arm 2, without employing an intermediate speed reduction mechanism. The robot is operated to move the chuck 4b to a desired position by appropriately controlling each of the prime movers described above.
With such a configuration, reaction forces will be applied acting between the first arm and second arm, due to differences between the respective amounts of angular rotation and levels of angular velocity and angular acceleration of the first arm and second arm. As a result, dynamic fluctuations of the load characteristics of the first prime mover and second prime mover will be produced, and as a result it is difficult to control the operation of the robot precisely, in a desired manner. It is possible to envisage applying compensation control such as to dynamically cancel the reaction forces produced between the first arm and second arm. However such control measures would substantially increase the manufacturing cost of such a robot.